[rules-users] Explanation of a decision

Hi, I'm working on expert system, automating one of the stages of optical design. Now, we're testing the system and we need a function, eхplaining a decision of the system: which rules has been fired, why they has been fired and so on. And I'm looking for a way to implement this feature. Has someone had an experience in implementing this kind of features? Or does someone know how it can be implemented? Thank you, Maxim Kolchin Laboratory of Intellectual Systems, National Research University ITMO, http://en.ifmo.ru